Because of the messiness of traditional inks, and in particular those inks in marking instruments used by children, there have been attempts to produce inks that are colorless until reacted with a specially treated surface or substrate. Traditionally, the preferred dyes used in these types of inks are leuco dyes chosen for their vivid, bold and intense colors. These leuco dyes are used in organic solvent-based compositions because most leuco dyes are insoluble in water. Some leuco dyes are water soluble, but those tend to require a large pH change from very high to very low, or vice versa, in order to effect color formation from the colorless state. This required pH change is generally undesirable. Although certain organic solvent-based compositions do provide the desired feature of reduced mess, the organic solvents used are relatively expensive, have undesirable odors, have a greasy feel and leave oily residues on paper or other surfaces.
As an alternative to organic solvent-based ink compositions, attempts have been made to utilize water as a solvent because of cost, odor elimination, and other benefits over the organic solvents. However, many of these types of dispersion ink compositions have slow color development and weak color intensity because the leuco dye cannot fully react with a color developer because the dyes are dispersed as solid particles or microcapsules in water. Therefore, it is difficult to obtain high color intensity with a water-based dispersion ink composition even when increased amounts of leuco dye are used.